1. Field of the Invention
The present invention relates to a purge control device for use in an internal combustion engine.
2. Description of the Related Art
It is well known in this field to fit a charcoal canister to an internal combustion engine as a part of a fuel vapor control system for the engine. The charcoal canister usually comprises a fuel vapor inlet connected to a fuel tank, a fuel vapor outlet connected to an intake passage in the vicinity of a throttle valve, and an air inlet connected to the intake passage upstream of the throttle valve and downstream of an air flow meter. In this system when the throttle valve is open, the fuel vapor outlet of the charcoal canister is connected to the intake passage downstream of the throttle valve, and consequently, a part of the air metered by the air flow meter at this time is fed into the charcoal canister, and the fuel component absorbed in activated carbons in the charcoal canister is desorbed by this air. The thus desorbed fuel component is then fed into the intake passage.
In this engine, however, when the temperature of exhaust gases fed into a catalyst of the exhaust emission system or the temperature of the catalyst bed is within a predetermined range, and when an air-fuel mixture fed into the engine cylinders temporarily becomes rich due to the supply of the purge gas purged from the charcoal canister, hydrogen sulfide (herein-after referred to as H.sub.2 S) is produced, and therefore, a problem arises in that an unpleasant and toxic odor is produced.